JP2006113228A - Objective lens and optical device using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an immersion type deep ultraviolet objective for which an inexpensive light source can be used because of correcting chromatic aberration without using a cemented lens and whose resolution is high, and provide an optical device using the same. <P>SOLUTION: The objective lens is used in a deep ultraviolet wavelength region, and every lens in the lenses L1 to L20 comprises a single lens, and is composed of two or more kinds of media (quartz and fluorite) different from each other. The objective is used in a state where space between an object surface and the lens L20 arranged nearest to the object side is filled with liquid (water) so as to observe an object as an enlarged image. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an objective lens and an optical device using the same, and more particularly to an objective lens used in a deep ultraviolet wavelength region near a wavelength of 250 nm and an optical device using the same for the purpose of observing a semiconductor wafer or a liquid crystal substrate. It is.

  In recent microscope apparatuses, particularly microscope apparatuses for observing semiconductor wafers and liquid crystal substrates, higher resolution objective lenses are required as the pattern line width becomes finer. The resolution R in such an objective lens can be expressed by the following equation (4), where λ is the wavelength of light involved in image formation and NA is the numerical aperture of the objective lens.

              R = 0.61 × (λ / NA) (4)

  From the above equation (4), it can be seen that in order to achieve a high resolution R in the objective lens, it is effective to generally take measures such as increasing the numerical aperture NA and shortening the wavelength λ. .

  By the way, some objective lenses are used in a deep ultraviolet wavelength region near a wavelength of 250 nm, and are configured only by a plurality of lenses formed of the same medium (in many cases, quartz) (hereinafter referred to as a first lens). And a lens made of different media (in many cases, quartz and fluorite) are bonded with a bonding agent (hereinafter referred to as a second type), and the like. .

  In the first type of objective lens, since chromatic aberration cannot be corrected in principle, it is relatively inexpensive. However, when a light source having a wavelength width, that is, a non-narrowed excimer laser or the like is used as a light source, There is a problem that the light condensing performance is remarkably deteriorated by chromatic aberration, and a predetermined resolution R determined by the wavelength λ and the numerical aperture NA as shown in the equation (4) cannot be obtained.

  Further, the second type objective lens can correct the chromatic aberration, and thus the above problem does not occur. However, there are few types of bonding agents that allow deep ultraviolet light to pass therethrough, and even if there are, for example, there are problems that most of the bonding agents have difficulty in bonding strength and workability. In addition, light of a low energy level such as a lamp may be used. However, when high energy light such as a laser beam is incident, the bonding agent deteriorates due to irradiation with deep ultraviolet light, and the internal transmittance of the objective lens is lowered, resulting in durability. There is a problem of impairing sex.

Therefore, in order to solve the problems that occur in these two types, the chromatic aberration is corrected using a quartz lens and a fluorite lens by using an unnarrowed laser with a wavelength of 248 nm as a light source. However, an objective lens in which both are not bonded with a bonding agent is disclosed (for example, see Patent Document 1). In addition, an objective lens that is a light source having a use wavelength of 193 nm, which is shorter than the use wavelength of 248 nm, has been put into practical use.
JP 2003-21785 A

  The numerical aperture of the objective lens described in Patent Document 1 described above is about 0.9, and it can be seen from Equation (4) that a line width of about 80 nm line & space can be resolved. However, at present, a microscope apparatus used for observing a semiconductor wafer or a liquid crystal substrate is required to resolve a thinner line width of about 65 nm line & space, and the objective lens of Patent Document 1 satisfies this requirement. It is difficult.

  In the objective lens having a wavelength of 193 nm, the light source is a narrow-band laser (for example, an ArF excimer laser), and although there is no problem of chromatic aberration correction, it is very expensive. There is a problem that the price of the apparatus is increased.

  The present invention has been made in view of such problems, and an immersion-type deep ultraviolet objective lens having a high resolution in which an inexpensive light source can be used by correcting chromatic aberration without using a cemented lens, and the same An object of the present invention is to provide an optical device using the above.

  In order to achieve such an object, the objective lens according to the present invention is used in the deep ultraviolet wavelength region, all the lenses are composed of a single lens, and all the lenses are composed of two or more different types of media, The object is magnified and observed by using a state in which the space between the object plane and the lens disposed closest to the object is filled with a liquid.

  In the present invention, the medium constituting the objective lens is any combination of fluoride crystal and quartz, at least two different fluoride crystals, and at least two different fluoride crystals and quartz. It is desirable to be.

  In the present invention, it is desirable to have a triplet configuration of a positive lens, a negative lens, and a positive lens in order from the image side.

  In the present invention, the triplet structure including a positive lens, a negative lens, and a positive lens in order from the image side includes a first lens group having a negative power as a whole, and a positive lens and a negative lens having different media. A second lens group having at least two or more pairs of lenses configured by disposing with an air interval, and having a positive power as a whole, wherein the focal length of the entire objective lens system is f, When the focal length of the lens group is f1, the total length of the objective lens is L, and the air space between the first lens group and the second lens group is D, the following equation is given: 0.01 ≦ | f / f1 | ≦ 0.3 (1) and 0.05 ≦ D / L (2) are desirably satisfied.

  In the present invention, it is desirable that the surface closest to the object side has a curvature.

  In the present invention, four or more concave lenses made of a medium having the largest dispersion among the media constituting the objective lens are included, and the focal lengths of these concave lenses are fmi (i = 1, 2, 3, 4,...), Respectively. , Pm = | Σ1 / fmi |, where f is the focal length of the entire objective lens system, and P = | 1 / f |, the following expression is satisfied: Pm / P> 1 (3) It is desirable to be configured as follows.

  In the optical apparatus according to the present invention, any of the objective lens described above and a lens barrel optical system assembled using a bonding agent, or a lens barrel optical system assembled without using a bonding agent. It is configured with

  As described above, according to the present invention, the configuration without using the cemented lens can solve all the problems caused by this, that is, all the problems caused by the irradiation of the lens cement with deep ultraviolet light. Moreover, various aberrations including chromatic aberration can be satisfactorily corrected, and an immersion-type deep ultraviolet objective lens having high resolution and an optical apparatus using the same can be realized.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The objective lens according to the present invention is used in the deep ultraviolet wavelength region, and all the lenses are composed of a single lens, and all the lenses are composed of two or more different types of media, and are arranged on the object surface and the most object side. The object is magnified and observed using a state in which the lens is filled with a liquid.

  As described above, in the objective lens of the present invention, the lenses having different media are not bonded using the bonding agent, and are all constituted by a single lens. Thereby, it is possible to avoid various problems caused by deterioration of the lens bonding agent upon receiving irradiation with deep ultraviolet light. The lens pair constituting the objective lens of the present invention has an effect close to that of a cemented lens in terms of aberration correction, and has a shape close to that of the cemented lens.

  In addition, the objective lens of the present invention is a so-called immersion type objective lens that uses an object surface and a lens disposed closest to the object side in a state of being filled with a liquid and observes the object in an enlarged manner. . In general, in an optical microscope, an immersion system in which the sample surface and the tip of the objective lens are filled with a liquid such as water or oil compared to a dry objective lens in which the sample surface and the tip of the objective lens are filled with air. It is well known that a higher resolution can be obtained with an objective lens. Therefore, the objective lens according to the present invention is used in immersion.

  In the objective lens of the present invention, all the lenses are composed of two or more different types of media. With such a configuration, chromatic aberration is corrected well.

  Incidentally, it is generally known that it is effective to use glass materials having different dispersions for chromatic aberration correction. However, when used in the deep ultraviolet wavelength region as in the present invention, since the internal transmittance of a general optical glass material is significantly reduced, the usable glass material is limited to fluoride crystals (for example, fluorite) and quartz. ing. Therefore, it is desirable that the medium constituting the objective lens of the present invention is a combination of fluoride crystal and quartz, at least two or more different fluoride crystals, and at least two or more different fluoride crystals and quartz. In the present invention, it is desirable to select calcium fluoride, lithium fluoride, strontium fluoride or the like as the fluoride crystal.

  The objective lens of the present invention includes an objective lens having a triplet configuration (hereinafter referred to as a first type objective lens, corresponding to claims 1 to 5) and an objective lens having no triplet configuration (hereinafter referred to as a second objective lens). The objective lens is classified into two types (corresponding to claims 1, 2, and 6). Hereinafter, these two types of objective lenses according to the present invention will be described.

  The objective lens according to the first type of the present invention has a triplet configuration including a positive lens, a negative lens, and a positive lens in order from the image side, and has a medium different from that of the first lens group having a negative power as a whole. It has at least two or more pairs of lenses configured by arranging positive and negative lenses with an air gap, and includes a second lens group having positive power as a whole. Several positive lenses are arranged in the vicinity of the surface closest to the object side of the second lens group.

  As described above, in the present invention, the first lens unit is configured to have a negative power as a whole, so that the light beam greatly expanded by the second lens unit can be returned to the parallel light beam without difficulty, and at the same time, the off-axis aberration The field curvature and coma aberration are corrected.

  Further, the first lens group has a triplet configuration, so that the lateral chromatic aberration that occurs during the correction is corrected very well. In particular, when quartz is used for the front lens of the second lens group, this triplet configuration works effectively.

  However, from the viewpoint of aberration correction, a fluoride crystal such as fluorite is used for the front lens of the second lens group (in the first and second embodiments described later, the positive lens L20 disposed closest to the object side). It is desirable to use it. However, since the object side surface of the front lens is immersed in the immersion liquid, it is desirable to use quartz when there is a concern about the liquid resistance and workability of the lens.

  The objective lens of the present invention corrects chromatic aberration by disposing at least two or more pairs of lenses, each of which is configured by disposing positive and negative lenses having different media with an air interval in the second lens group. This is because, as described above, since the objective lens is used in the deep ultraviolet wavelength region, usable glass materials are limited.

  In addition, since the objective lens of the present invention has a large numerical aperture (about 1.24), the objective lens is composed of three pseudo-joined lenses rather than the two lenses pseudo-joined with the lens pair. It is possible to correct axial chromatic aberration more effectively.

  In addition, by arranging several positive lenses near the surface closest to the object side of the second lens group, the light incident on the optical system can be refracted and generated from the second lens group. Spherical aberration is minimized.

  In the first type objective lens as described above, in order to keep the balance of each aberration in a very good state, the focal length of the entire objective lens system is f, the focal length of the first lens group is f1, and the objective lens When the total length of the lens is L (specifically, the distance from the first surface to the final surface of the objective lens) and the air space between the first lens group and the second lens group is D, the following equations (1) and (2) It is desirable to satisfy

0.01 ≦ | f / f1 | ≦ 0.3 (1)
0.05 ≦ D / L (2)

  The conditional expression (1) defines the power distribution of the first lens group with respect to the entire objective lens. If the upper limit value of conditional expression (1) is exceeded, the negative power of the first lens group becomes too strong, and the balance with the second lens group having a large number of lenses and a fairly strong positive power as a whole is large. This is not desirable because it causes deterioration of spherical aberration. On the other hand, if the lower limit of conditional expression (1) is not reached, the negative power of the first lens group is insufficient, and the spherical aberration generated from the second lens group cannot be completely corrected, which is not desirable.

  The conditional expression (2) is very important for setting the triplet configuration of the first lens group. If the lower limit value of the conditional expression (2) is not reached, the conditional expression (2) is widened well for the second lens group. When returning the emitted light beam to a parallel light beam, field curvature and coma are generated, which is not desirable. The purpose of arranging the triplet configuration in the first lens group of the present optical system is to suppress lateral chromatic aberration, but if the lower limit of conditional expression (2) is not reached, the purpose will not be achieved, which is desirable. Absent.

  In the objective lens of the present invention which is the first type, it is desirable that the object side surface of the lens arranged closest to the object side, that is, the lens surface in contact with the immersion liquid has a curvature. This is because various aberrations can be further reduced by such a configuration. In the conventional objective lens, it has been considered that if the surface closest to the object side (lens surface in contact with the immersion liquid) is used with a curvature, bubbles may be generated on the lens surface. It has been confirmed that there is almost no possibility.

  On the other hand, the objective lens of the present invention that is the second type has at least two or more pairs of lenses configured by disposing positive and negative lenses having different media at an air interval. The same as the objective lens. In the second type of objective lens, the medium having the largest dispersion among the media constituting the objective lens is formed (for example, in the third embodiment described later, the medium constituting the objective lens is fluorite. (The medium having the largest dispersion is quartz because it is one of quartz.) It includes four or more concave lenses, and the focal lengths of these concave lenses are fmi (i = 1, 2, 3, 4...), And Pm = When | Σ1 / fmi |, f is the focal length of the entire objective lens system, and P = | 1 / f |, it is desirable to satisfy the following expression (3).

              Pm / P> 1 (3)

  Conditional expression (3) relates to the arrangement of the concave lens in the objective lens that is the second type. If the lower limit value of conditional expression (3) is not reached, achromaticity becomes insufficient, and the contrast of the image is reduced. This is undesirable because it causes a drop.

  The optical device of the present invention is a microscope device, for example, according to the first or second type objective lens and the intensity of the light source (according to the intensity of light reaching the lens barrel optical system). The lens barrel optical system assembled using a bonding agent or the lens barrel optical system assembled without using a bonding agent is provided. Regarding the selection of the lens barrel optical system, if the power of the light reaching the lens barrel optical system is extremely large, a problem due to the deterioration of the bonding agent due to the irradiation of deep ultraviolet light occurs (similar to the above objective lens). It is desirable to use one assembled without using any agent. In addition, when the power of the light reaching the lens barrel optical system is not so strong, it is more desirable because it is possible to use a product assembled using a bonding agent, and rather the manufacturing cost can be suppressed.

  Embodiments according to the present invention will be described below with reference to the accompanying drawings.

  In any of the embodiments, the immersion liquid used for the objective lens according to the present invention, that is, the object-side surface of the lens disposed closest to the object side from the sample surface (in the first and second embodiments, the values in the table) In the third embodiment, water is used as the liquid that fills the gap up to the surface number 36) in the table.

  In addition, since the objective lens of the present invention is designed at infinity, in the following examples, the order is shown in the reverse order to the actual light traveling direction.

  First, an objective lens according to a first type of the present invention will be described using two examples, a first example and a second example. As shown in FIG. 1 for the lens configuration diagram of the first embodiment and in FIG. 3 for the lens configuration of the second embodiment, all the lenses are composed of a single lens in any embodiment, and in order from the image side, A triplet configuration of a positive lens L1, a negative lens L2, and a positive lens L3 having a concave surface facing the image side. The first lens group G1, which has a negative power as a whole, and a positive lens and a negative lens with different media are separated from each other with an air space. The second lens group G2 has seven lens pairs P1 to P7 configured by arranging them and has a positive power as a whole.

  The first lens group G1 includes a positive meniscus lens L1, a biconcave lens L2, and a positive meniscus lens L3 from the image side. The second lens group G2 includes, from the image side, a lens pair P1 including a biconvex lens L4 and a biconcave lens L5, a lens pair P2 including a biconvex lens L6 and a biconcave lens L7, and a lens pair including a biconvex lens L8 and a biconcave lens L9. P3, a lens pair P4 composed of a biconvex lens L10 and a biconcave lens L11, a lens pair P5 composed of a biconvex lens L12 and a biconcave lens L13, and a lens pair P6 composed of the biconcave lens L13 and the biconvex lens L14 (that is, three lenses) L12, L13 and L14 form two pairs of lenses P5 and P6), a biconvex lens L15, a lens pair P7 composed of a biconcave lens L16 and a biconvex lens L17, a positive meniscus lens L18 having a concave surface facing the object side, It consists of L19 and L20. The lens surface closest to the object, that is, the object-side surface of L20 (surface number 40 described later) is configured to have a concave curvature on the object side.

(First embodiment)
The objective lens of the first embodiment according to the present invention will be described with reference to FIGS. The specifications of each lens in the objective lens of the first example according to the present invention are shown in Table 1 (however, the unit of length is all mm). In this specification table, the first column m is the number of each optical surface from the object side (hereinafter referred to as surface number), the second column r is the radius of curvature of each optical surface, and the third column d is each optical surface. The distance on the optical axis from the first to the next optical surface (or image surface) (hereinafter referred to as the surface interval), the fourth column represents the glass material, and the fifth column represents each lens component. In the table, f represents the focal length of the entire objective lens system, NA represents the numerical aperture, and n represents the refractive index of the immersion liquid with respect to the reference beam (248 nm). These are the same in other embodiments. .

  In addition, the focal length f, the radius of curvature r, the surface interval d, and other length units of the entire objective lens system listed in all the following specification values are “mm” unless otherwise specified. ing. However, since the optical system can obtain the same optical performance even if it is proportionally enlarged or reduced, the unit is not limited to “mm”, and other appropriate units can be used.

(Table 1)
Aberration correction range in the deep ultraviolet wavelength region: 248nm ± 3nm
NA = 1.25
Refractive index of immersion liquid: n = 1.396342
mr d glass material
1 -39.907 1.50 Quartz L1
2 -10.955 5.15 (Air)
3 -126.105 0.75 Fluorite L2
4 5.058 14.85 (Air)
5 -15.595 3.90 Quartz L3
6 -13.326 17.60 (Air)
7 25.945 2.85 Fluorite L4
8 -17.974 0.78 (Air)
9 -11.539 0.75 Quartz L5
10 56.794 0.15 (Air)
11 15.085 3.25 Fluorite L6
12 -17.399 0.25 (Air)
13 -15.249 0.74 Quartz L7
14 24.439 0.16 (Air)
15 15.085 3.25 Fluorite L8
16 -17.399 0.25 (Air)
17 -15.249 0.74 Quartz L9
18 24.439 0.16 (Air)
19 15.085 3.25 Fluorite L10
20 -17.399 0.25 (Air)
21 -15.249 0.74 Quartz L11
22 24.439 0.15 (Air)
23 13.527 3.15 Fluorite L12
24 -17.258 0.25 (Air)
25 -15.125 0.71 Quartz L13
26 11.394 0.27 (Air)
27 13.000 2.45 Fluorite L14
28 -25.653 0.13 (Air)
29 9.024 2.65 Fluorite L15
30 -30.248 0.40 (Air)
31 -17.986 0.67 Quartz L16
32 14.823 0.07 (Air)
33 8.955 1.75 Fluorite L17
34 -120.372 0.13 (Air)
35 4.340 1.51 Fluorite L18
36 7.769 0.12 (Air)
37 2.480 1.28 Fluorite L19
38 3.242 0.07 (Air)
39 1.032 1.00 Quartz L20
40 8.000 0.22 Immersion liquid (Conditional expression values)
f = 1.98
f1 = -36.62
D = 17.60
L = 78.08
(Conditional expression)
(1) 0.01 ≦ | f / f1 | = 0.0541 ≦ 0.3
(2) 0.05 ≦ D / L = 0.2254

  Thus, in the first embodiment, it can be seen that all the conditional expressions (1) and (2) are satisfied.

  FIG. 2 shows spherical aberration, field curvature, and distortion in the objective lens according to Example 1 of the present invention. In each aberration diagram, NA represents a numerical aperture, Y represents a maximum image height, x represents a wavelength of 248 nm, y represents a wavelength of 251 nm, and z represents a wavelength of 245 nm. In the field curvature, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. The explanation of the above aberration diagrams is the same in the other examples.

  As is apparent from the respective aberration diagrams shown in FIG. 2, it can be seen that various aberrations are satisfactorily corrected in the objective lens of this example.

(Second embodiment)
The objective lens according to the second embodiment of the present invention will be described with reference to FIGS. Since the configuration of the objective lens according to the present embodiment has been described above (see FIG. 3), description thereof is omitted here. Table 2 shows the specifications of each lens in the objective lens according to Example 2 of the present invention.

(Table 2)
Aberration correction range in the deep ultraviolet wavelength region: 248nm ± 3nm
NA = 1.24
Refractive index of immersion liquid: n = 1.378487
mr d glass material
1 -21.196 1.80 Quartz L1
2 -8.989 4.00 (Air)
3 -42.629 1.00 Fluorite L2
4 5.100 12.70 (Air)
5 -14.670 4.50 Quartz L3
6 -13.670 14.50 (Air)
7 33.847 3.60 Fluorite L4
8 -14.530 0.80 (Air)
9 -11.680 1.00 Quartz L5
10 115.492 0.15 (Air)
11 18.970 3.80 Fluorite L6
12 -19.920 0.60 (Air)
13 -15.261 1.00 Quartz L7
14 37.862 0.16 (Air)
15 17.016 3.80 Fluorite L8
16 -25.286 0.45 (Air)
17 -18.541 1.00 Quartz L9
18 21.600 0.22 (Air)
19 19.005 3.80 Fluorite L10
20 -21.600 0.40 (Air)
21 -24.638 1.00 Quartz L11
22 30.503 0.15 (Air)
23 15.000 3.90 Fluorite L12
24 -24.000 0.30 (Air)
25 -19.900 1.00 Quartz L13
26 12.301 0.52 (Air)
27 14.370 3.90 Fluorite L14
28 -20.396 0.13 (Air)
29 10.895 3.90 Fluorite L15
30 -33.227 0.53 (Air)
31 -19.410 1.00 Quartz L16
32 12.800 0.07 (Air)
33 11.170 2.40 Fluorite L17
34 -73.638 0.13 (Air)
35 4.301 2.00 Fluorite L18
36 7.680 0.12 (Air)
37 2.582 1.35 Fluorite L19
38 3.212 0.07 (Air)
39 1.031 1.00 Quartz L20
40 7.997 0.22 Immersion liquid (Conditional expression values)
f = 2.00
f1 = -25.26
D = 14.50
L = 82.75
(Conditional expression)
(1) 0.01 ≦ | f / f1 | = 0.0792 ≦ 0.3
(2) 0.05 ≤ D / L = 0.1752

  Thus, it can be seen that in the second embodiment, all the conditional expressions (1) and (2) are satisfied.

  FIG. 4 shows spherical aberration, field curvature, and distortion in the objective lens according to Example 2 of the present invention. As is apparent from the respective aberration diagrams shown in FIG. 4, it is understood that various aberrations are satisfactorily corrected in the objective lens of this example.

(Third embodiment)
Next, an objective lens according to a third example of the second type of the present invention will be described with reference to FIGS. In the lens configuration diagram of the third example, as shown in FIG. 5, all the lenses are configured by a single lens, and in order from the image side, a negative lens L1, a lens pair P1 to P6, and positive lenses L12 and L13. Lens pair P7 and positive lenses L16 to L18. Note that the seven pairs of lenses P1 to P7 have a configuration in which positive lenses and negative lenses having different media are arranged with an air gap, as in the first type.

  More specifically, the objective lens of the third embodiment includes, in order from the image side, a negative meniscus lens L1 having a concave surface facing the object side, a lens pair P1 including a biconvex lens L2 and a biconcave lens L3, the biconcave lens L3, and both A lens pair P2 composed of a convex lens L4, and a lens pair P3 composed of the biconvex lens L4 and a biconcave lens L5 (ie, four lenses L2, L3, L4 and L5 form three pairs of lenses P1, P2 and P3). A lens pair P4 composed of a biconvex lens L6 and a biconcave lens L7, a lens pair P5 composed of a biconvex lens L8 and a biconcave lens L9, a lens pair P6 composed of a biconvex lens L10 and a biconcave lens L11, biconvex lenses L12 and L13, both A lens pair P7 composed of a concave lens L14 and a biconvex lens L15, positive meniscus lenses L16 and L17 with a concave surface facing the object side, and an image side And a plano-convex lens L18 having its surface. The specifications of each lens in the objective lens of the third example according to the present invention are shown in Table 3 below.

(Table 3)
Aberration correction range in the deep ultraviolet wavelength region: 248nm ± 3nm
NA = 1.25
Refractive index of immersion liquid: n = 1.396342
mr d glass material
1 19.497 0.51 Fluorite L1
2 7.204 1.67 (Air)
3 11.747 1.40 Fluorite L2
4 -7.578 0.08 (Air)
5 -6.706 0.45 Quartz L3
6 7.400 0.05 (Air)
7 7.760 1.55 Fluorite L4
8 -7.528 0.15 (Air)
9 -5.895 0.50 Quartz L5
10 91.244 0.17 (Air)
11 9.472 1.60 Fluorite L6
12 -8.105 0.10 (Air)
13 -7.203 0.50 Quartz L7
14 12.252 0.45 (Air)
15 11.323 1.70 Fluorite L8
16 -7.336 0.10 (Air)
17 -7.175 0.50 Quartz L9
18 16.680 0.82 (Air)
19 7.578 1.80 Fluorite L10
20 -12.003 0.15 (Air)
21 -9.684 0.50 Quartz L11
22 9.441 0.75 (Air)
23 10.210 1.65 Fluorite L12
24 -14.513 0.10 (Air)
25 5.594 1.88 Fluorite L13
26 -17.975 0.30 (Air)
27 -9.276 0.50 Quartz L14
28 8.749 0.05 (Air)
29 7.104 1.24 Fluorite L15
30 -28.859 0.10 (Air)
31 2.922 1.13 Fluorite L16
32 5.595 0.10 (Air)
33 1.640 0.95 Fluorite L17
34 2.218 0.05 (Air)
35 0.750 0.75 Fluorite L18
36 ∞ 0.20 Immersion liquid (conditional expression corresponding value)
fm1 = -6.84, fm2 = -10.87, fm3 = -8.84,
fm4 = -9.80, fm5 = -9.32, fm6 = -8.77,
Pm = | Σ1 / fmi | = 0.6747 (where i = 1, 2,..., 6)
f = 2.00
P = | 1 / f | = 0.5
(Conditional expression)
(3) Pm / P = 1.349> 1

  Thus, in the third example, it can be seen that the conditional expression (3) is satisfied.

  FIG. 6 shows spherical aberration, field curvature, and distortion in the objective lens according to the third example of the present invention. As is apparent from the respective aberration diagrams shown in FIG. 6, it can be seen that various aberrations are satisfactorily corrected in the objective lens of this example.

(Fourth embodiment)
A microscope apparatus according to a fourth embodiment in which the objective lens according to the present invention is used will be described with reference to FIG.

  The microscope apparatus 20 includes a light source 1, a collector lens 2, a filter 3, an aperture stop 4, a field stop 5, a condenser lens 6, a first beam splitter 7, and an objective lens 8 (the first to third lenses described above). Example), a discharge nozzle 9, a suction nozzle 10, a test object (semiconductor wafer) 11, a liquid receiver 12, a stage 13, a first reflection mirror 14, and a lens barrel optical system (second optical system). (Objective lens) 15, second reflecting mirror 16, second beam splitter 17, eyepiece 18, and image sensor 19.

  It should be noted that each of the objective lenses 8 of the above-described embodiments is an infinity correction type. Therefore, in the microscope apparatus 20 of the present invention, the lens barrel optical system (second objective lens) 15 is disposed on the image side of the objective lens 8, and a finite optical system is obtained by combining the objective lens 8 and the lens barrel optical system 15. Is forming.

  The microscope apparatus 20 having the above configuration uses epi-illumination, and the light emitted from the light source 1 is collected by the collector lens 2, and only light having a predetermined wavelength width travels through the filter 3, and the aperture stop 4. An image of the light source 1 is formed thereon. Then, the image travels through the field stop 5, relays the image of the light source 1 onto the exit pupil of the objective lens 8 via the condenser lens 6 and the first beam splitter 7, and as a parallel light beam by the objective lens 8 in the horizontal plane and in the vertical direction. A test object (for example, a semiconductor wafer) 11 on the movable stage 13 is illuminated.

  The aperture stop 4 is arranged at a conjugate position via the exit pupil of the objective lens 8 and the illumination optical systems 1 to 6, and the thickness of the illumination light beam, that is, the incident angle range of the light that illuminates the object 11 to be examined. It prescribes.

  The objective lens 8 is an immersion objective lens as described above. When the object to be examined 11 and the tip of the objective lens 8 are immersed in a liquid (immersion), the aberration of the optical system is reduced. Designed to be corrected. For this reason, in the vicinity of the tip of the objective lens 8, in order to fill a space between the tip of the lens 8 and the test object 11 with a liquid such as pure water, a discharge nozzle 9 for discharging a predetermined amount of liquid; A suction nozzle 10 for sucking in the liquid at the end of the observation is provided.

  It is desirable to provide a liquid receiver 12 below the object 11 to prevent liquid from spilling from the stage 13 and splashing the liquid to other parts. This is because liquid is discharged from the discharge nozzle 9 in an attempt to observe the periphery of the test object 11, but if the liquid spills from the test object 11 without forming a liquid droplet, the liquid is slid on the sliding surface of the stage 13 or the like. This is for preventing the stage 13 from operating properly due to falling onto the stage 13 and floating or sticking to the stage 13.

  Subsequently, the light emitted from the illuminated object 11 travels as a parallel light beam by the objective lens 8 and enters the lens barrel optical system 15 via the first beam splitter 7 and the first reflection mirror 14. . Then, the light that has passed through the lens barrel optical system 15 is split into a light beam that travels in the direction of the eyepiece lens 18 and a light beam that travels in the direction of the image sensor 19 by the second beam splitter 17 via the second reflection mirror 16. Is done. Here, among the divided lights, the light traveling in the direction of the eyepiece 18 forms an image at the visual field position and is used for visual observation. The light traveling in the direction of the image sensor 19 forms an image on the element 19 so that an electronic image of the sample can be obtained.

  In this embodiment, as shown in FIG. 7, the second beam splitter 17 is used to distribute light to the eyepiece 18 and the image sensor 19, but the present invention is not limited to this. For example, the second beam splitter 17 can be put in and out so that the light can reach either the visual field position of the eyepiece 18 or the imaging surface of the imaging device 19.

  Here, the lens barrel optical system 15 used in the microscope apparatus 20 will be described with reference to FIGS. FIG. 8 is a lens configuration diagram of a lens barrel optical system (hereinafter referred to as a first lens barrel optical system 15A) having a configuration in which no cemented lens is used, and FIG. 9 is a lens barrel optical system having a configuration in which a cemented lens is used ( Hereinafter, it is a lens configuration diagram of a second lens barrel optical system 15B).

  In the microscope apparatus 20 according to the present embodiment, any of the objective lenses shown in the first to third embodiments is used as the objective lens 8, and these use a light source having a relatively large power. As a result, in the microscope apparatus 20, it is desirable to use the first lens barrel optical system 15 </ b> A configured without using the bonding agent as shown in FIG. 8 (that is, using no bonding lens). However, in the microscope apparatus 20, when a light source having a relatively small power, such as a mercury lamp, is used, for example, the influence of inconvenience caused by the use of the bonding agent is low, and the manufacturing cost can be suppressed rather. It is desirable to use the second lens barrel optical system 15B constructed using a bonding agent as shown in FIG. 9 (that is, using a cemented lens).

  First, the first lens barrel optical system 15A constructed without using a bonding agent will be described with reference to FIG. The first lens barrel optical system 15A is constructed from the positive meniscus lens L21, the biconvex lens L22, and the biconcave lens L23 in this order from the object side (from the left side in FIG. 8 and from the objective lens 8 side in FIG. 7). Constructed, no cemented lens is used. Table 4 shows the specifications of each lens of the first lens barrel optical system 15A.

(Table 4)
Focal length f = 400 of the entire first lens barrel optical system
mr d glass material
1 105.620 2.00 Quartz L21
2 34.660 1.00 (Air)
3 35.170 3.00 Fluorite L22
4 -200.000 82.52 (Air)
5 -1555.000 2.00 Quartz L23
6 78.175 200.00 (Air)

  Next, the second lens barrel optical system 15B constructed using a bonding agent will be described with reference to FIG. The second lens barrel optical system 15B includes, in order from the object side (from the left side in FIG. 9 and from the objective lens 8 side in FIG. 7), a cemented lens including a positive meniscus lens L31 and a biconvex lens L32. It is composed of a biconcave lens L33. Table 5 shows the specifications of each lens of the second lens barrel optical system 15B.

(Table 5)
Focal length f = 400 of the entire system of the second lens barrel optical system
mr d glass material
1 92.349 2.00 Quartz L31
2 35.180 3.00 Fluorite L32
3 -289.851 80.00 (Air)
4 -1555.088 2.00 Quartz L33
5 77.402 200.00 (Air)

  The present invention as described above is not limited to the above embodiment, and can be improved as appropriate without departing from the gist of the present invention.

It is sectional drawing which shows the structure of the objective lens which concerns on 1st Example of this invention. FIG. 3A is a diagram illustrating various aberrations of the objective lens according to Example 1 of the present invention, in which (A) shows spherical aberration, (B) shows field curvature, and (C) shows distortion. It is sectional drawing which shows the structure of the objective lens which concerns on 2nd Example of this invention. FIG. 6 is a diagram illustrating various aberrations of the objective lens according to Example 2 of the present invention, in which (A) shows spherical aberration, (B) shows field curvature, and (C) shows distortion. It is sectional drawing which shows the structure of the objective lens which concerns on 3rd Example of this invention. FIG. 4A is a diagram illustrating various aberrations of the objective lens according to Example 3 of the present invention, in which (A) shows spherical aberration, (B) shows field curvature, and (C) shows distortion. 1 is a schematic view of a microscope apparatus according to the present invention. It is sectional drawing which shows the structure of the lens barrel optical system used with the microscope apparatus which concerns on this invention. It is sectional drawing which shows the structure of the other barrel optical system used with the microscope apparatus which concerns on this invention.

Explanation of symbols

G1 1st lens group G2 2nd lens group L Each lens component 1 Light source 2 Collector lens 3 Filter 4 Aperture stop 5 Field stop 6 Condenser lens 7 First beam splitter 8 Objective lens 9 Discharge nozzle 10 Suction nozzle 11 Test object (semiconductor) Wafer)
DESCRIPTION OF SYMBOLS 12 Liquid receptacle 13 Stage 14 1st reflective mirror 15 Lens barrel optical system 16 2nd reflective mirror 17 2nd beam splitter 18 Eyepiece 19 Imaging element 20 Microscope apparatus (optical apparatus)

Claims (7)

Used in the deep ultraviolet wavelength region, all lenses consist of a single lens,
All the lenses are composed of two or more different media,
Use in a state where the space between the object surface and the lens arranged closest to the object is filled with liquid,
An objective lens characterized by magnifying and observing an object.   The medium constituting the objective lens is a combination of any one of fluoride crystals and quartz, at least two or more different fluoride crystals, and at least two or more different fluoride crystals and quartz. The objective lens according to claim 1.   The objective lens according to claim 1, wherein the objective lens has a triplet configuration of a positive lens, a negative lens, and a positive lens in order from the image side. From the image side,
A first lens group having the triplet configuration including a positive lens, a negative lens, and a positive lens, and having a negative power as a whole;
A second lens group having at least two or more pairs of lenses configured by disposing positive lenses and negative lenses having different media with an air interval, and having a positive power as a whole;
The focal length of the entire objective lens system is f, the focal length of the first lens group is f1, the total length of the objective lens is L, and the air space between the first lens group and the second lens group is D. When the following formula,
0.01 ≦ | f / f1 | ≦ 0.3 (1)
0.05 ≦ D / L (2)
The objective lens according to claim 1, wherein the following condition is satisfied.   The objective lens according to claim 1, wherein a surface closest to the object side has a curvature. Including four or more concave lenses made of a medium having the largest dispersion among the media constituting the objective lens;
The focal lengths of these concave lenses are fmi (i = 1, 2, 3, 4...), Pm = | Σ1 / fmi |, the focal length of the entire objective lens system is f, and P = | 1 / f | The following formula
Pm / P> 1 (3)
The objective lens according to claim 1, wherein the following condition is satisfied. The objective lens according to any one of claims 1 to 6,
An optical device comprising either a lens barrel optical system assembled using a bonding agent or a lens barrel optical system assembled without using a bonding agent.

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